gpio: dt-bindings: Add GPIO on top of generic pin control

Traditionally, firmware will provide a GPIO interface or a pin control
interface.  However, the SCMI protocol provides a generic pin control
interface and the GPIO support is built on top of that using the normal
pin control interfaces.  Potentially, other firmware will adopt a
similar generic approach in the future.

Document how to configure the GPIO device.

Signed-off-by: AKASHI Takahiro <takahiro.akashi@linaro.org>
Signed-off-by: Dan Carpenter <dan.carpenter@linaro.org>
Reviewed-by: Linus Walleij <linusw@kernel.org>
Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@oss.qualcomm.com>
Signed-off-by: Linus Walleij <linusw@kernel.org>

Author: AKASHI Takahiro

Documentation/devicetree/bindings/gpio/pin-control-gpio.yaml

@@ -0,0 +1,59 @@
+# SPDX-License-Identifier: GPL-2.0-only OR BSD-2-Clause
+%YAML 1.2
+---
+$id: http://devicetree.org/schemas/gpio/pin-control-gpio.yaml#
+$schema: http://devicetree.org/meta-schemas/core.yaml#
+
+title: Pin control based generic GPIO controller
+
+description:
+  The pin control-based GPIO will facilitate a pin controller's ability
+  to drive electric lines high/low and other generic properties of a
+  pin controller to perform general-purpose one-bit binary I/O.
+
+maintainers:
+  - Dan Carpenter <dan.carpenter@linaro.org>
+
+properties:
+  compatible:
+    const: scmi-pinctrl-gpio
+
+  gpio-controller: true
+
+  "#gpio-cells":
+    const: 2
+
+  gpio-line-names: true
+
+  gpio-ranges: true
+
+  ngpios: true
+
+patternProperties:
+  "^.+-hog(-[0-9]+)?$":
+    type: object
+
+    required:
+      - gpio-hog
+
+required:
+  - compatible
+  - gpio-controller
+  - "#gpio-cells"
+  - gpio-ranges
+  - ngpios
+
+additionalProperties: false
+
+examples:
+  - |
+    gpio {
+        compatible = "scmi-pinctrl-gpio";
+        gpio-controller;
+        #gpio-cells = <2>;
+        ngpios = <4>;
+        gpio-line-names = "gpio_5_17", "gpio_5_20", "gpio_5_22", "gpio_2_1";
+        gpio-ranges = <&scmi_pinctrl 0 30 4>;
+        pinctrl-names = "default";
+        pinctrl-0 = <&keys_pins>;
+    };